am: remember --rerere-autoupdate setting

Save the rerere-autoupdate setting so that it is remembered after
stopping for the user to resolve conflicts.
Signed-off-by: NPhillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/am.c

@@ -431,6 +431,14 @@ static void am_load(struct am_state *state)
 	read_state_file(&sb, state, "utf8", 1);
 	state->utf8 = !strcmp(sb.buf, "t");
 
+	if (file_exists(am_path(state, "rerere-autoupdate"))) {
+		read_state_file(&sb, state, "rerere-autoupdate", 1);
+		state->allow_rerere_autoupdate = strcmp(sb.buf, "t") ?
+			RERERE_NOAUTOUPDATE : RERERE_AUTOUPDATE;
+	} else {
+		state->allow_rerere_autoupdate = 0;
+	}
+
 	read_state_file(&sb, state, "keep", 1);
 	if (!strcmp(sb.buf, "t"))
 		state->keep = KEEP_TRUE;
@@ -1003,6 +1011,10 @@ static void am_setup(struct am_state *state, enum patch_format patch_format,
 	write_state_bool(state, "sign", state->signoff);
 	write_state_bool(state, "utf8", state->utf8);
 
+	if (state->allow_rerere_autoupdate)
+		write_state_bool(state, "rerere-autoupdate",
+			 state->allow_rerere_autoupdate == RERERE_AUTOUPDATE);
+
 	switch (state->keep) {
 	case KEEP_FALSE:
 		str = "f";